There are a number of applications, usually medical, in which solid particles are to be extracted from a liquid/solid slurry. The particles to be examined may be captured by a filter or may be passed by the filter while larger, undesired particles are blocked. One specific medical application includes the separation of parasite larvae and eggs from a stool sample placed in a specimen vial filled with a fixative or preservative. The devices used for this application are typically called "stool transportation and filtration systems". One improvement over previous devices is discussed in U.S. Pat. No. 4,675,110 assigned to the same entity as this application. In that device, one improvement involved the equalization of pressure between a collection vessel and an attached receptacle vessel.
There are some devices on the market for collecting and filtering such samples, but few offer a safe, closed system in which collection and transfer occurs without any chance of spillage. Some devices spill easily, others include filters susceptible to blockage. Still others require additional components in order to collect and agitate a sample or will only work properly with specially fabricated components. Most are difficult to use and may confuse the technician, or worse, the patient.